The present invention relates to an optical mouse for moving a cursor appearing on the screen of a CRT (cathode-ray tube) display.
A cursor position instructing unit called a "mouse" is available for freely moving a cursor on a CRT screen in the direction of X and Y axes. As the mouse is moved about on a flat plate called a "mouse pad", the cursor is moved in the direction of the X and Y axes in coincidence with the movement of the mouse.
Examples of a conventional mouse are a mechanical mouse disclosed by Japanese Published Utility Model Application No. 7467/1979 and an optical mouse disclosed by Japanese Patent Application No. 500777/1983.
The mechanical mouse is designed so that a ball rotatably provided in the mouse body is rolled in the direction of the X and Y axes by moving the mouse on a table. The cursor is moved in the directions of the X and Y axes according to the amounts of rotation of an X-axis direction detecting ring and a Y-axis direction detecting ring which rotate in frictional contact with the ball.
On the other hand, in the optical mouse, line detectors composed of light-emitting elements and light-detecting elements are employed to read a grid pattern of vertical and horizontal lines of different colors, for instance, a grid pattern having green lines extending in the direction of the X axis and red lines extending in the direction of the Y axis.
In more detail, the mechanical mouse includes a ball which is rolled on the mouse pad, at least two detecting rings operated in association with the ball, and a device for converting the rotations of the detecting rings into electrical signals. As a result, the mechanical mouse is disadvantageous in that it is intricate in construction and in that the accuracy of its mechanical components and their assembly must be high. On the other hand, in the optical mouse, two groups of lines of different colors are used to distinguish the directions of the X and Y axes from each other, and two light source or filters of different colors must be provided to read the two groups of lines. The two groups of lines are formed on the same surface and are separately detected by a time-division method whereby the light sources and the light-detecting elements are operated alternately and in a synchronized manner. Therefore, the optical mouse is also disadvantageous in that it is intricate in construction and high in manufacturing cost. Furthermore, since the directions of the X and Y axes are detected in a time-division manner, if the speed of movement of the mouse is too high, it may not be possible to count the lines correctly, and hence errors are caused in reading the lines.
The movement of the mouse on the pad is in proportion to the movement of the cursor on the CRT screen. The movements of the mouse and the cursor are two dimensional, and therefore the positions of the mouse and the cursor can be geometrically determined in X-Y coordinates. The position of the mouse on the mouse pad is determined by the number of lines counted in the direction of the Y axis, while the position of the cursor is determined on the CRT screen in correspondence to the position of the mouse.
If the line pattern indicating the direction of the X axis and the line pattern indicating the direction of the Y axis are on the same surface, the mouse cannot distinguish a signal obtained by counting the lines in the direction of the X axis and a signal obtained by counting the lines in the direction of the Y axis from each other without making the line patterns different in color, reflectivity, or the like. Especially when the direction of movement of the mouse on the pad is changed by 90.degree. it is difficult to correctly count the lines. This difficulty can be alleviated by making the line pattern in the direction of the X axis and the line pattern in the direction of Y axis different in reflectivity. According to this method, changes of the direction of movement of the mouse can be detected from the difference in reflectivity between the line patterns due to the difference between the quantities of light reflected from the two line patterns. However, in converting the difference between the quantities of light into an electrical signal, it is impossible to convert it directly into a digital signal. Therefore, the practice of this method requires an intricate signal processing technique whereby the difference is converted into an analog signal and the analog signal thus obtained is converted into a digital signal.